#include <fstream>

using namespace std;

#define NMAX 2000005

int N;
bool b[NMAX];

int main()
{
	ifstream in("ciur.in");
	ofstream out("ciur.out");
	in >> N;
	for(int i = 0; i < NMAX; ++i)
		b[i] = true;
			
	for(int i = 2; i <= NMAX / 2; ++i)
		if(b[i])
			for(int j = 2 * i; j < NMAX; j += i)
				b[j] = false;
				
	int n = 0;
	
	for(int i = 2; i <= N; ++i)
		if(b[i])
			++n;
	
	out << n;
	
	return 0;
}